The present invention relates to ophthalmologic surgery and more particularly, relates to a method and apparatus for cutting an oblong corneal flap to facilitate laser in situ keratomileusis (LASIK) surgery to correct hyperopia.
A normal ametropic eye includes a cornea, lens and retina. The cornea and lens of a normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disorder known as ametropia, which is the inability of the lens and cornea to focus the far point correctly on the retina. Typical types of ametropia are myopia (near sightedness), hypermetropia or hyperopia (far sightedness), and astigmatism.
A myopic eye has either an axial length that is longer than that of a normal eye, or a cornea or lens having a refractive power stronger than that of the cornea and lens of a normal eye. This stronger refractive power causes the far points to be projected in front of the retina. Conversely, a hypermetropic or hyperopic eye has either an axial lens shorter than that of a normal eye, or a lens or cornea having a refractive power less than that of a lens and cornea of a normal eye. This lesser refractive power causes the far point to be focused on the back of the retina. An eye suffering from astigmatism has a defect in the lens or shape of the cornea and is incapable of sharply focusing images on the retina.
Various approaches have been taken to correct such disorders by properly focusing light onto the retina. Glasses can be used to correct such disorders but are sometimes considered awkward and inconvenient, particularly for individuals with an active lifestyle. Although contact lenses have addressed some of the inconveniences of glasses, contact lenses present additional problems with care and maintenance and possibly irritation or damage to the eye.
More recently, different types of surgery have been used to change the shape of the cornea and correct eye disorders. Examples of such surgical procedures include automated lamellar keratectomy (ALK) and laser in situ keratomileusis (LASIK). According to both of these procedures, a thin layer of the cornea is cut using a microsurgical instrument known as a microkeratome. Removing the thin layer of cornea allows the live cornea to be reshaped in a way that corrects the disorder. Examples of microkeratomes are disclosed in U.S. Pat. No. 5,133,726 to Ruiz et al., U.S. Pat. No. 5,964,776 to Peyman, and U.S. Pat. No. 6,007,553 to Hellenkamp et al., all of which are incorporated herein by reference.
The use of the LASIK procedure to correct hyperopia presents a unique problem. As shown in FIG. 1, the cornea 12 of an eye 10 is cut to form a corneal flap 16. The corneal flap 16 is folded over at a connecting portion 18 to expose the freshly cut, inner corneal surface 20. To affect correction of hyperopia, laser light 2 is directed at an ring-shaped region 22 on the inner corneal surface 20, as shown in FIG. 2. When the corneal flap 16 is repositioned and reattached, the ablation of the cornea 12 in this ring-shaped region 22 increases the curvature of the cornea and corrects the hyperopia.
One problem encountered with this procedure is the need for a large treatment area 22 which begins to approach the vertical regions of the cornea which contain blood vessels 19. If a sufficiently large circular corneal flap 16 is cut, there is a significant risk of corneal bleeding due to cutting of the blood vessels 19. An additional problem adds to the risk of severing a blood vessel which is that the connecting portion 18 of the corneal flap may interfere with the treatment region 22. Therefore, there is a tension between making the corneal flap large enough to accommodate the treatment region 22 while not cutting corneal blood vessels 19.
Accordingly, there is a need for a method and apparatus for cutting the corneal flap in a way that allows the cornea to be shaped without interfering with the connecting portion of the flap and without significant risk of severing or cutting blood vessels.
The present invention features a method of performing LASIK surgery to correct hyperopia. The method comprises the steps of positioning a cornea holding device over a live cornea to stabilize the live cornea such that a portion of the live cornea extends through an oblong opening in the cornea holding device. An oblong corneal flap is then cut from the live cornea extending through the oblong opening in the cornea holding device and is folded over to expose a freshly cut, inner corneal surface. A laser is then directed at a ring-shaped region on the inner corneal surface to ablate the inner corneal surface at the ring-shaped region. The oblong corneal flap is then repositioned onto the inner corneal surface to allow the oblong corneal flap to reattach. The oblong shape of the corneal flap allows the ring-shaped region to be ablated without interfering with the connecting portion of the corneal flap.
The present invention also features a method of cutting an oblong corneal flap to facilitate reshaping of a live cornea. The method comprises the steps of positioning a cornea holding device over a live cornea to stabilize the live cornea such that a portion of the live cornea extends through an oblong opening in the corneal holding apparatus. A cutting tool is then moved across the portion of the live cornea to separate the portion of the live cornea, while leaving a connecting portion of the live cornea intact to form the oblong corneal flap.
The present invention also features an apparatus for cutting an oblong corneal flap comprising a cornea holding device having an oblong opening for receiving an oblong portion of a live cornea. A cutting tool is positioned above the cornea holding device for cutting the oblong portion of the live cornea to form the oblong corneal flap.